Method of making single-cast, high-temperature thin wall structures having a high thermal conductivity member connecting the walls

ABSTRACT

Disclosed is an integral single-cast multi wall structure including a very thin wall and a second thin wall. There is a passageway interposed between the pair of walls of the structure, and a high thermal conductivity member extends into said passageways and thermally couples the walls. The high thermal conductivity member increases the heat transfer between the walls of the structure. The present invention further includes a method for casting an integral structure having very thin walls that utilizes the high thermally conductive member in the casting process to hold the pattern and cores in alignment.

RELATED APPLICATIONS

This is a divisional application of U.S. patent application Ser. No.08/896,883 filed Jul. 18, 1997, which issued as U.S. Pat. No. 5,924,483on Jul. 20, 1999. U.S. Pat. application Ser. No. 08/896,883 is adivisional application of U.S. patent application Ser. No. 08/474,308filed on Jun. 7, 1995, which issued as U.S. Pat. No. 5,810,552 on Sep.22, 1998. U.S. patent application Ser. No. 08/474,308 is acontinuation-in-part of U.S. patent application Ser. No. 08/201,899filed Feb. 25, 1994, which issued as U.S. Pat. No. 5,545,003 on Aug. 13,1996. U.S. patent application Ser. No. 08/201,899 is a divisional ofU.S. patent application Ser. No. 07/838,154 filed Feb. 18, 1992 whichissued as U.S. Pat. No. 5,295,530 on Mar. 22, 1994.

FIELD OF THE INVENTION

This invention relates to single-cast, high-temperature, thin wallstructures and methods of making the same. More particularly thisinvention relates to thin wall hollow structures having high thermalconductivity members connecting therebetween that are capable ofwithstanding impinging gases at high temperatures.

BACKGROUND OF THE INVENTION

Thick walled one-piece alloy structures are disclosed in U.S. Pat. Nos.3,806,276 and 3,192,578. Laminated structures having thin walls capableof withstanding of high temperature impinging gases have heretofore beenknown. By way of example, such structures are disclosed in U.S. Pat.Nos. 4,245,769; 4,042,162; 4,004,056; 3,963,368; 3,950,114; 3,933,442;3,810,711; 3,732,031; 3,726,604; 3,698,834; 3,700,418; 3,644,059;3,644,060; 3,619,082, 3,616,125; 3,610,769; 3,606,769; 3,606,572;3,606,572; 3,606,573; 3,584,972; 3,527,544; 3,529,905 and 3,497,277. Thethin walls of such structures are laminated to another thin wall or to asubstantially thicker structure by brazing, welding or otherwisebonding. The laminating process involves high temperature brazing,welding or bonding materials that directly affect the alloy or otherwiselimit the overall high temperature performance of the structure.Further, these thin wall layers often have holes formed therein bymechanical means or etching which is time consuming, labor intensive andexpensive. Although these laminated thin wall structures are capable ofwithstanding impinging gases at temperatures higher than the meltingpoint of alloys which the structures are made from, the process ofmaking the structures is time consuming, labor intensive and extremelyexpensive.

Many prior art methods of casting hollow structures utilize ceramiccores. It has been generally accepted that these core must have adensity sufficiently low enough such that the core is compressive sothat it gives as molten allow solidifies around the core. It hasgenerally been accepted that if the core has a density above 60 to 70percent, the core will be crushed and broken by molten alloy whichsolidifies around it. It has also generally been accepted that coreshaving a thickness less than 0.03 inches with such low density lesswould be crushed and broken during casting. The density of prior artceramic cores ranges from about 50 to about 60 percent.

Although 100 percent quartz rods having 100 percent density have beenused, such use has been limited to making bent and straight holes orcentral passageways. heretofore, a high density ceramic core (above 70to 99 percent plus density) has not been used to make a radialpassageway. Generally, in turbine engine components such as turbineblades, such radial passageways parallel the outer thin wall of thecomponent or turbine blade.

It is generally accepted that the use of a high density material for alarge core will break the metal. As molten alloy solidifies around alarge high density core, the metal shrinks faster than the core and willbreak due to the high density core. Thus, those skill in the art use lowdensity cores to compensate for the fast rate of shrink of the moltenmetal and to prevent the metal from breaking.

Another problem recognized by those skilled in the art is the problem ofshape distortion during casting. Heretofore, it has been generallyaccepted that this shape distortion of the casted part is caused by whatis known as “mold buckle”. This “mold buckle” occurs in the process ofbuilding up the shell around the core and pattern. If one of thesuccessive shell layers does not sufficiently dry, the layer moves awayfrom the pattern causing the mold to “buckle” and causes a distortedcasting shape. Heretofore, it was not recognized that casting shapedistortion could be caused by shell creep.

In prior art methods of making laminated thin wall structures such asgas turbine blades, the thin walls are provided by metal which has beencold rolled to a very thin thickness. The cold-rolled metal is thenetched or machined to provide small holes in the surface thereof. Thesmall holes provide a cooling air film over the thin wall as the gasturbine blade is impinged with hot gases. This cold-rolled metal must beformed and bonded (or welded sufficiently to provide heat transfer fromthe thin wall to the main body of the blade) in a curved shape toproduce the outer wall of a turbine blade. The forming process mayresult in the distortion of the holes in the wall. If the holes are notproperly positioned, or the metal not sufficiently bonded, it ispossible to develop hot spots at certain section on the blade whichwould be undesirable and would limit production yields. Further, thecold-rolled material must be later heat treated which also couldpossibly result in varying heat transfer properties across the surfaceof the blade which also would be undesirable.

Other casting problems are caused by ceramic cores which are extremelybrittle and fragile. These problems increase with decreasing thicknessand density.

Heretofore, there has been a need for single-cast, high-temperature,thin wall hollow structures and means for making the same which isquick, relatively inexpensive and not labor intensive. A means forsatisfying this need has theretofore escaped those skilled in the art.

SUMMARY OF THE INVENTION

The present invention includes the discovery of a variety of phenomenaand agencies which gave rise to an idea of a means for repeatably andreliably producing or casting thin multi wall hollow structures havinghigh thermal conductivity members connecting therebetween withdimensional accuracy and having the wall thickness less than about 0.03inches. The following statements, by way of example, highlight thediscoveries which are part of the present invention as a whole.

The invention includes the discovery that the problem of creep of aceramic shell can be solved by controlling the injection pressure of themolten alloy into a cavity. The injection pressure may be controlled asa function of time to cast walls having a thickness less than about 0.03inches without shell creep.

The invention includes the discovery that the injection pressure of analloy into a cavity can be varied as a function of time by using acontrol orifice to bleed the head pressure off after the thin cavity hasbeen filled.

The invention includes the discovery that very thin passageways of about0.005 to 0.015 inches can be formed using a thin core having a densitygreater than about 70 percent, and preferably about 99 percent orgreater.

The invention includes the discovery that a thin core having a thicknessof about 0.005 to 0.015 inches and a density greater than about 70percent will not be crushed and broken when surrounded by solidifyingalloy.

The invention includes the discovery that such thin cores can be used toform narrow radial passageways, having a width of about 0.005 to about0.015 inches, in casting and such passageway can be formed substantiallyparallel to a thin outer wall having a thickness of about 0.005 to about0.03 inches.

The invention includes the discovery that cores having a thickness of0.005 to 0.015 inches can be used in core making, pattern making andcasting process without reducing yields.

The invention includes the discovery that a structure can be cast usinghigh thermal conductivity rods, preferably NiAl, having a minimumdimension in the range of about 0.005 to about 0.55 inches that connectbetween the walls in the thin wall structure and hold theabove-described thin core in place during casting. These high thermalconductivity rods can be of any shape.

The invention includes the discovery that a pocket can be drilled into aceramic core so as to receive and hold such as a narrow diameter rod.

The invention includes the discovery that a single-piece, hollowmulti-wall structure having a very thin outer wall, an inner wall and avery thin passageway therebetween can be cast using a ceramic core,narrow rod and thin ceramic core construction.

The invention includes the discovery that a very thin curved core can beheld in position in a casting mold by forming a first ceramic core;coating the first ceramic core with wax or plastic pattern where metalis desired; placing the very thin curved ceramic core on the pattern;drilling a hole through the very thin ceramic core, pattern and into thefirst ceramic core to form a pocket; inserting a rod through the hole sothat the rod is received in the pocket in the first ceramic core;covering the very thin ceramic core with a thin layer of wax or plasticpattern where a thin wall of metal is desired; forming a hole throughthe thin layer of wax and into the thin ceramic core so as to form anangled pocket in the first core at a predetermined position where forceis needed to keep the thin ceramic core in its curved shape; inserting aportion of an outer rod through the hole in the thin layer of wax so asto be received in a pocket from in the main ceramic core or in the thincore so that upon casting the structure a passage is provided throughthe thin wall and into the cavity formed by the main core; and coveringthe thin layer of wax and the other portion of the outer rod with aceramic shell.

The invention includes the discovery that defects in the walls of acasting, made using a ceramic shell, can be avoided by sandblasting theabove-described thin layer of wax on the face closest to the ceramicshell.

The invention includes the discovery of a means for producingsingle-cast, thin wall structures having smooth outer surfaces andhaving wall thicknesses as narrow as about 0.005 inches.

The invention includes the discovery of a single-cast, thin wall hollowstructure capable of withstanding impinging gases at temperatures ashigh as 4300° F. or higher.

Another advantage of the present invention is that finer details can bemade in the thin ceramic core using a laser due to the high density ofthe core.

The present invention can be utilized to make structures having multiplethin walls each having a thickness less than about 0.03 inches which areconnected by high thermal conductivity rods.

The present invention has a lighter weight, higher temperaturecapabilities and greater strength then the laminated thin wallstructures of the prior art and is greatly more economical to produce.

It is possible using the techniques of the present invention to makemulti-wall structures, that are connected together by high thermalconductivity rods, having more than 20 thin walls each having athickness less than 0.03 inches. These and other discoveries, objects,features and advantages of the present invention will be apparent fromthe following brief description of the drawings, detailed descriptionand appended drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a prior art casting mold;

FIG. 2 is a sectional view of a prior art casting mold after the moldhas creeped;

FIG. 3 is a graphic illustration of the process of varying chargepressure with time of the present invention.

FIG. 4 is an illustration of a casting mold of the present invention;

FIG. 5 is an illustration of a casting mold, pattern, core and rodcombination of the present invention;

FIG. 6 is an illustrating of a thin ceramic core of the presentinvention;

FIG. 7 is an illustration of a method of forming single crystal alloystructures;

FIG. 8 is an illustration of a multi-wall structure of the presentinvention;

FIG. 9 is an illustration of a jet engine having nozzles made accordingto the present invention;

FIG. 10 is an illustration of an atmospheric air/space craft having aleading edge made from a material according to the present invention;

FIG. 11 is a cross-section of a prior art film cool turbine-blade;

FIG. 12 is a cross-section of a single piece, single cast turbine-bladehaving a thin outer wall according to the present invention; and

FIG. 13 is an graphic illustration of various turbine-blade designsdeveloped over time verse practical operating turbine inlet temperatures(° F.) for gas turbine engines using the various turbine-blade designs.

DESCRIPTION OF THE PREFERRED EMBODIMENT

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiment illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, such alternatives and furthermodifications in the illustrated device, and such further applicationsof the principles of the invention as illustrated therein beingcontemplated as would normally occur to one skilled in the art to whichthe invention relates.

The techniques of the present invention may be used to produce thinwalled hollow structures having high thermal conductivity membersconnecting between the walls using equiaxed, directionally solidifiedand single crystal alloy processes. A variety of techniques are knownfor producing equiaxed, directionally solidified and single crystalalloy structures. The present invention is particularly suitable forproducing very thin walled structures using single crystal castingtechniques. One such single crystal casting technique is illustrated inFIG. 7, which shows a casting mold 100 carried on a water cooled chillplate 102 and received in a mold heater 104. A casting furnace 106includes a vacuum system 108 and an induction melting crucible 110 forpouring molten alloy in the mold 100. Once the molten alloy is poured inthe mold, the mold is slowly removed from the furnace by an elevator112.

Generally, for single crystal processing, the molding temperature ispreferably heated to at least 2800° and the single crystal superalloy isheated to 2800° F. and the single crystal is grown slowly at about 10inches/hr. Generally, for equiaxed processes, the mold temperature isheated to about 1800° F. and the equiaxed alloy temperature is heated to2800° F. and the alloy solidified at 1 mm/min.

Various types of superalloy compositions and manufacturers of suchcompositions are known to those skilled in the art. Most alloys ofinterest are complicated mixtures of nickel, chromium, aluminum andother elements.

Prior attempts to cast multi-wall structures having at least one wallless than 0.03 inches thick have been foiled by what has been known as“shell creep.” In order to get molten alloy to completely fill narrowpassages less than 0.03 inches thick, a substantial amount of headpressure is necessary. However, the ceramic shell used in such castingprocesses is not sufficiently strong enough to withstand the headpressure needed to fill these narrow passages. As a result, the headpressure causes the walls of the shell to creep outwardly thusdistorting the mold and rendering the part unacceptable., This problemis particularly troublesome when casting at high temperature with slowsolidification such as single crystal investment casting.

FIG. 1 illustrates a cross-sectional view of a standard mold beforeinjecting molten alloy under pressure. The portion of FIG. 1 form pointsA-B represent the alloy charge reservoir, points B-C a charge runner,and points C-D the actual shape of the part to be cat. FIG. 2illustrated a cross-sectional view of the distortion of the mold due tosustained pouring or injecting head pressure of the molten alloy. As canbe appreciated from FIG. 2, maintaining the head pressure duringinjection of the molten alloy, causes the wall to become substantiallythicker than desired. Points D-E illustrate the distortion of thecasting shell due to “shell creep:” under substantial head pressure. The“shell creep” phenomenon precludes the casting of a structure withdimensional accuracy using prior processes.

The present invention includes the discovery that the problem of “creep”of a ceramic shell can be solved by varying the injection pressure of amolten alloy into a cavity, having a thickness less than about 0.03inches, as a function of time. This concept is graphically illustratedin FIG. 3. One means of accomplishing this is illustrated in FIG. 4.

FIG. 4 illustrates a ceramic shell 10 having a part mold 11 having acavity 12 for producing a structure with a wall having a thickness lessthat about 0.03 inches. Molten alloy is injected into the cavity andallowed to solidify to form a desired structure. An alloy charge line 14is located about the area of the mold cavity designated for the desiredstructure. Molten alloy is delivered from a reservoir 16 defined bycontainer 15 through the molten alloy charge line 14 to the structurecavity of the mold. A charge pressure control means may be a controlorifice 18 that is located above the structure cavity of the mold andconnected to the alloy charge line. The charge pressure control meansmay be a bleed line 20 to remove excess alloy once the cavity has beenfilled and to reduce the head pressure of the molten alloy thuseliminating the undesirable “creep” of the ceramic shell. The bleed line20 communicates with an excess alloy reservoir 22. Preferably the excessalloy reservoir 22 is located immediately below the alloy reservoir 16and is defined by a hollow column 24 which supports container 15. Aplurality of port molds 11 may be positioned radially around the column24 with associated charge lines 14 and bleed lines 20 as describedabove. The typical range of head pressure for casting a wall having athickness of less than 0.03 inches ranges from about 10 inches to about14 inches of a nickel-based superalloy having a density of about 0.03lbs./in.³. The technique may be used to fill cavities less than 0.03inches thick, and up to 5 feet high and 2 feet wide.

The invention includes the discovery that very thin passageways of about0.005 to about 0.015 inches wide, can be formed using a thin core havinga density greater than about 70 percent, and preferably about or greaterthan 99 percent. The present invention uses thin cores having athickness less than about 0.005 to about 0.020 inches and having adensity greater than about 99 percent. These cores may be made out of aceramic material of a plastic material. It has been discovered that thehigh density of such thin cores gives the thin core sufficient strengthto withstand core, wax pattern, mold and casting processes. A suitablematerial for use in such thin cores is a silica (SiO₂) material,commonly called quartz. The surface of the core may be patterned toprovide pedestalsor indentations by machining or preferably by laserpatterning. The very thin ceramic core having a thickness less thanabout 0.03 inches may be shaped before or after making holes in it by,for example, a process of “creep” forming over a contoured die.

The very thin ceramic core can be made form a variety of materialscapable of withstanding the alloy casting temperatures and which can beeasily removed with a strong acid or base of can be burned out ash free.A preferred material for the very thin ceramic core is quartz. FIG. 6illustrates a suitable thin ceramic core having a pattern formed by alaser on the surface thereof. The pattern forms channels and pedestalsin the cast part to increase surface area for heat exchange.

The present invention includes the discovery that a thin wall structurecan be cast using high thermal conductivity rods 30′ having a diameterof about 0.09 to about 0.55 inches that connect between a pair of wallsin the multi wall structure. During the process of manufacturing thesingle cast thin wall structure the rods 30′ hold the above-describedthin core in place during casting. The rods 30′ may be of a variety ofshapes in addition to the substantially cylindrical rods depending onthe desired objectives. In the preferred embodiment the high thermalconductivity rods 30′ are of a different material than the thin wallstructure, and the rods 30′ have a higher thermal conductivity than thethin wall structure. In a more preferred embodent the rods 30′ are madeof NiAl, or of other similar material. The high thermal conductivityrods 30′ connect to at least one of the walls of the multi wallstructure and extend into the passageway interposed between a pair ofthe walls.

With reference to FIGS. 5 and 8, there is illustrated the high thermalconductivity rod 30′. It is understood that a plurality of high thermalconductivity rods 30′ are contemplated in the multi wall structure ofthe present invention. The rods 30′ are metallurgically bonded to thesurrounding multi wall alloy structure as the metal fills in around therods 30′. The high thermal conductivity rods 30′ facilitate heattransfer between the walls of the structure. The rods 30′ may extendinto the pattern 36 or may just abut it depending upon the objectivedesired. High thermal conductivity rod 30″ passes through the thinceramic core 32 and abuts the inner surface 44 a of casting shell 44 andthe outer surface 28 a of the main core 28. Further, rod 30″ ismetallurgically bonded to the surrounding multi-wall alloy structure asthe metal fills in thereround. U.S. Pat. No. 5,295,530 is incorporatedherein by reference. It is contemplated that in an alternate form of thepresent invention that a combination of holes and high thermalconductivity rods may be integrated into the walls of the mutli wallstructure.

In order to cast the multi wall structure the high thermal conductivityrods 30′ must be received in a pocket 26 formed in the core 28. Thepocket may be formed in the core during the core molding process or maybe subsequently formed in the molded core by a variety of means such asdrilling or directing a laser beam on the core.

The invention includes the discovery that in one embodiment a pocket 26can be drilled into a ceramic core 28 so as to receive and hold theabove-described narrow diameter high thermal conductivity rod 30′ in theceramic core if the core to be drilled is free of the normal protectivecoating used in the art. The present invention includes a process whichavoids using a protective coating on the ceramic core. As illustrated inFIG. 5, the ceramic core 28 free of protective coating is drilled toprovide a pocket 26 for receiving and holding a narrow diameter highthermal conductivity rod 30′ in the ceramic core. The high thermalconductivity rod 30′ will provide after casting a thermal link betweenthe walls of the structure, and the rod 30′ passes through the thinceramic core 32 to hold the thin ceramic core 32 in a fixed relationshipbetween the casting shell 32 and the main core 28. The pocket 26 is madesufficiently large enough to receive the rod 30′ yet small enough tofirmly hold it in place and withstand any thermal expansion of the rod30′ or ceramic core during the casting process. Generally a clearanceranging from about 0.0005 to about 0.001 inches greater than thediameter of the rod is sufficient.

The present invention includes a method for holding the very thin,curved core 32 in position in the casting process. According to thepresent invention, a first ceramic core 28 is prepared and coated with afirst pattern 34 of wax or plastic where metal is desired. Then acurved, very thin core 32 is placed on the first pattern 34 andinitially located with locating pins (not shown). The locating pins arepositioned near the corners of the thin core and extend into the patternso as to temporarily hold the thin core in position while thesubsequently described hole making process takes place. A hole isdrilled thorugh the very thin ceramic core 32, pattern 34 and into thefirst ceramic core 28 to form a pocket 26 in the first core 28 forreceiving and holding in place a small diameter high thermalconductivity rod 30′. A small diameter high thermal conductivity rod 30′is inserted through the hole so that the rod 30′ is received in thepocket formed in the first ceramic core 28. The very thin ceramic coreis then covered with a thin pattern 36 of wax or plastic (or othersuitable material) where a thin wall of metal is desired. Then the holesare formed at an angle through the thin pattern 36 and into the thinceramic core to form a pocket 38 at a predetermined position where forceis needed to keep the thin ceramic core in its curved shape. Althoughthe thin ceramic core may be already curved, the core has a resiliencyor elasticity that cause it to want to move out of a curved shape suchas that needed to make a gas-turbine blade. An outer rod 30 is insertedthrough the hole in the pocket 38 of the thin ceramic core. Rod 30 ismade of quartz or a similar material. Finally, the thin pattern 36 andthe other portion of the outer rod 42 are covered with a ceramic shell44.

The thin core may also be held in position by a geometric relationshipof the core and holding rods. A rod may extend through a thin curvedcore so that the longitudinal axis of the rod is at an angle of ninetydegrees or greater to a line tangential to the curved core surface at apoint near the longitudinal axis of the rod. This arrangement preventsthe core from moving.

A relatively longer substantially cylindrical high thermal conductivityrod 46 extends through the thin pattern 36, thin core 32, first pattern34 and is carried by the main core 28. A labyrinth for air flow may beformed by a first rod 48 (quartz) held on one end by the casting shell44 and extending through the thin pattern 36 and the thin core 32. Asecond rod 50 (quartz) is positioned a distance laterally from the firstrod 48, is held on one end by the main core 28 and extends through thefirst pattern 34 and the thin core 32. So that when the part is cast andthe rods and cores are removed, air may flow from the outer surface ofthe part perpendicularly through the hole formed by rod 48 in the thinwall associated with the thin pattern 36, parallel to the thin wallthrough the passageway formed by the thin core 32 and perpendicularthrough the hole formed by rod 50 in the wall associated with the firstpattern 34 out to the void left by the main core 28. It is understoodthat the high thermal conductivity rods are not designed to be removedafter casting. This type of labyrinth provides enhanced air contact withthe thin wall associated with the thin pattern 36 and provide enhancedcooling of the thin wall such that the wall, in combination with otherfeatures described herein, can withstand impinging gases at temperaturesof 4300° F. and greater. Further, it is contemplated that the labrinthcan be eliminated and replaced by a pair of high thermal conductivityrods. Thereafter the patterns are removed. In the case of wax patterns,the entire mold is preheated to cause the wax to flow out of the moldleaving a cavity for molten alloy and so that the cores are held firmlyin place. The alloy is then cast in the mold as described above and thenon high thermal conductivity rods and cores are removed, for example,with a caustic solution.

The present invention includes the discovery that defects in the wall ofa casting made using a ceramic shell can be avoided by reducing thesurface tension of the above-described thin layer of wax or plastic onthe face closest to the ceramic shell. One way to reduce the surfacetension of the wax or plastic pattern is to sandblast the pattern'souter surface.

Once the above-described thin layer of wax has been coated over the thinceramic core, the thin layer of wax and other portions of the outer rodare covered with a ceramic shell. The ceramic shell covering is made byfirst dipping the thin layer of wax in a slurry having ceramic particlesin a colloidal silica vehicle. A suitable ceramic powder may have a meshsize of about 325. The mold is then dipped into dry ceramic refractorypowder to give strength to the shell. The process of dipping the moldinto a ceramic slurry followed by dry ceramic refractory powder isrepeated until a sufficient thickness of the shell is achieved, forexample, a thickness of about ½ inches. The ceramic slurry and drypowder are dried in an oven at a temperature of about 72°-78° F., at 10percent to 30 percent relative humidity during each dipping step. Inthis dried state, the shell may produce dust particles having a sizeranging from about {fraction (1/1000)} to about {fraction (3/1000)}inch. It has been discovered that when the mold is heated the waxexpands upon heating to accumulate ceramic dust particles whichindividually have a size ranging from about {fraction (1/1000)} to about{fraction (3/1000)} inch in sufficient amounts so as to produce in thecast structure surfaces defects having a size of {fraction (20/1000)}inch or greater. It has also been discovered that this problem can beeliminated by altering the surface tension of the wax or plastic priorto coating with the ceramic shell. Particularly suitable sandblastingmaterial is 120 grit A1203 used at a pressure ranging from about 5 toabout 10 psi.

Using the above-described techniques, it is possible to produce asingle-cast, thin wall structure having smooth outer surfaces and a wallthickness as narrow as about 0.005 inches. FIG. 8, illustrates a singlepiece, thin walled, gas-turbine blade according to the present inventionwith portions removed. FIG. 9 is a sectional view of a single-piece,multi-wall structure according to the present invention. Thissingle-cast, thin wall structure is capable of withstanding impinginggases at temperatures as high as 4300° F. The techniques of the presentinvention can be utilized to produce a variety of products which will bereadily apparent from those skilled in the art including gas turbineblades such as jet engine nozzles 100 (illustrated in FIG. 9), leadingedge 104 of wings and similar structures for above atmosphere air/spacecraft 102 (illustrated in FIG. 10). It is understood that the termairfoil will be used herein to refer to either a gas turbine blade or agas turbine vane.

According to the present invention, a variety of thin walled hollowstructure may be cast having equiaxed, single crystal and directionalsolidified structures. Forequiaxed structures the very thin wall mayhave a thickness ranging from about {fraction (10/1000)} to about{fraction (40/1000)} inches and preferably about {fraction (10/1000)} toabout {fraction (15/1000)} inches. For single crystal and directionalsolidified structures the very thin wall may have a thickness of about{fraction (3/1000)} to about {fraction (40/1000)} inches, preferably{fraction (3/1000)}-{fraction (20/1000)} inches, an most preferablyabout {fraction (3/1000)} to about {fraction (10/1000)} inches. Thinwalled hollow structure having such thickness can be cast withdimensional accuracy using the processes of the present invention.

Then the invention or an element of the invention is defined in terms ofranges or proportions, such is intended to convey the invention asincluding the entire range, or any sub-range or multiple sub-rangeswithin the broader range. For example, when an element of the inventionis described as containing about 5 to about 95 weight percent ofcomponent A. such is intended to convey the invention as also includingfrom about 5 to 40 weight percent A, from about 20 to about 30weightpercent A, and from about 90 to about 95 weight percent A. For example,the expression A₅₋₉₀B20-70 is intended to convey the invention asincluding the composition of A₅₋₂₀B₂₋₀₄, A₈₅₋₉₀B 20-25 and A₄₃B₅₇. Forexample, the expression “having a thickness ranging from about {fraction(3/1000)} to about {fraction (40/1000)} inches” is intended to conveythe invention as including a thickness ranging from about {fraction(3/1000)}-{fraction (5/1000)} inches, and from about {fraction(5/1000)}-{fraction (15/1000)} inches.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it is being understoodthat only the preferred embodiment has been shown and described and thatall changes and modifications that come within the spirit of theinvention are desired to be protected.

What is claimed:
 1. A method of making a multi-wall alloy structurecomprising: providing a main core corresponding to a void in thestructure; providing a high thermal conductivity member having a higherthermal conductivity than a thin wall in the structure which has athickness of less than 0.03 inches; providing a first removable patternmaterial covering the main core corresponding to a first wall of thestructure; providing a thin core having a density greater than 70percent in fixed relationship to the main core so as to correspond to athin passageway in the structure; providing a second removable patternmaterial covering the thin core so as to correspond to the thin wall inthe structure; inserting the high thermal conductivity member throughthe thin core so that it contacts the removable patterns; surroundingthe second removable pattern with a casting mold so as to define theouter surface of the thin wall; removing the patterns to leave the coresin fixed relationship with each other and the casting mold; charging thecasting mold with molten alloy and varying charge pressure with time sothat the thin wall is formed without causing the casting mold to creep;solidifying the molten alloy and removing the casting mold and the coresto provide the multi-wall alloy structure with the high thermalconductivity member connected thereto.
 2. The method of claim 1, furthercomprising: altering surface tension of the second removable patternmaterial to minimize formation of defects in the structure.
 3. Themethod of claim 2, wherein said altering surface tension includes sandblasting a surface of the second removable pattern before saidsurrounding, and wherein in said providing the second removable patternmaterial includes wax.
 4. The method of claim 1, further comprising:inserting a first member through the thin core and the first removablepattern, wherein one end of the first member is held at one end by themain core; inserting a second member through the second removablepattern and into the thin core; and removing the first member and thesecond member after said solidifying the molten alloy.
 5. The method ofclaim 4, wherein said removing the first member and the second memberoccurs during said removing the casting mold and the cores.
 6. Themethod of claim 4, wherein in said providing the main core includes ahole, and wherein in said inserting the first member the one end of thefirst member is received in the hole.
 7. The method of claim 6, whereinsaid providing the hole in the main core includes drilling the hole. 8.A method comprising: providing a main ceramic core; providing a firstnarrow rod of a high thermal conductivity material, wherein the highthermal conductivity material has a higher thermal conductivity than athin wall of a formed structure; covering the main ceramic core with afirst pattern where an alloy is to be cast; placing a very thin core onthe pattern, the thin core having a thickness less than about 0.02inches and a density greater than about 70 percent, and the thin corepositioned to have a curved shape; providing a hole through the thincore, the first pattern and into the main core to form a pocket in themain core to receive a portion of the first narrow rod; inserting aportion of the first narrow rod through the thin core so that thelongitudinal axis of the first narrow rod and the outer surface of thethin core away from the main core are at substantially right angles,through the first pattern and so that a portion of the rod is firmlyreceived in the pocket of the main core; covering the thin core with asecond pattern where an alloy is to be cast; providing a hole throughthe second pattern and into the thin core to provide an angled pocket inthe thin core for receiving a second rod at a predetermined positionwhere force is needed to keep the thin core in a position such that thethin core has the curved shape; inserting a second rod in the hole inthe second pattern and so that the second rod is received in the pocketof the thin core; surrounding the second pattern with a casting mold sothat the casting mold carries one end of the second rod and so that uponremoval of the patterns the cores are held in a fixed relationship toeach other and the casting mold, and the thin core retains its shape;removing the patterns; casting the alloy into the casting mold; andremoving the casting mold and the cores to provide the formed structurewith the first narrow rod connected thereto.
 9. The method of claim 8,further comprising: sand blasting an outer surface of the second patternbefore said surrounding.
 10. The method of claim 8, further comprising:inserting a first airflow member through the thin core and the firstpattern, wherein one end of the first airflow member is held by the maincore; inserting a second airflow member through the second pattern andinto the thin core; and removing the first airflow member and the secondairflow member after said casting the alloy.
 11. A method comprising:providing a casting pattern; forming narrow holes through the patternhaving a diameter ranging from about 0.009 to about 0.55 inches;providing a plurality of rods having a high thermal conductivity whichis higher than a thermal conductivity of a thin wall in a formedstructure; inserting the plurality of rods through the holes to provideoutwardly extending rod ends, each of the rods having a diameterslightly less than the diameter of the holes; forming a casting moldaround the pattern so that the outwardly extending rod ends are held bythe casting mold; removing the pattern; casting molten alloy in the voidleft by the pattern and solidifying the molten alloy; removing thecasting mold to provide the formed structure having a portion of theplurality of rods received therein and connected with the solidifiedmolten alloy.
 12. The method of claim 11, further comprising: sandblasting a portion of the pattern which contacts the casting mold beforesaid forming the casting mold.
 13. The method of claim 11, furthercomprising: inserting a first member into the pattern; inserting asecond member into the pattern; and removing the first member and thesecond member after said solidifying.
 14. A method of making amulti-wall alloy structure, comprising: inserting a high thermalconductivity member having a first thermal conductivity into a castingpattern; providing a mold around the casting pattern so that the highthermal conductivity member is supported by the mold; removing thecasting pattern to create a void; casting molten alloy into the voidleft by the casting pattern; solidifying the molten alloy, wherein thesolidified molten alloy has a second thermal conductivity, and whereinthe first thermal conductivity of the high thermal conductivity memberis greater than the second thermal conductivity of the solidified moltenalloy; and removing the mold to provide the structure having at least aportion of the high thermal conductivity member provided within thesolidified molten alloy and connected with the solidified molten alloy.15. The method of claim 14, wherein in said providing the mold includesa main core which contacts a portion of the casting pattern, a thin coreprovided within the casting pattern and a shell provided around thecasting pattern.
 16. The method of claim 15, further comprising:providing the casting pattern, wherein said providing the castingpattern includes covering the main core with a first pattern materialbefore said providing the thin core and covering the thin core with asecond pattern material, and wherein casting pattern includes the firstpattern material and the second pattern material.
 17. The method ofclaim 16, further comprising: sand blasting an outer surface of thesecond pattern after said covering the thin core.
 18. The method ofclaim 15, wherein said providing the main core includes forming a pocketwithin the main core to support the high thermal conductivity member.19. The method of claim 18, wherein said forming the pocket includesdrilling the pocket into the main core.
 20. The method of claim 18,wherein said forming the pocket includes molding the main core to havethe pocket.
 21. The method of claim 18, wherein said providing the thincore includes forming a hole within the thin core to support the highthermal conductivity member, and wherein said inserting the high thermalconductivity member includes positioning the high thermal conductivitymember within the pocket of the main core and the hole of the thin coreso as to prevent the thin core from moving.
 22. The method of claim 15,wherein said providing the thin core includes forming a hole within thethin core to support the high thermal conductivity member.
 23. Themethod of claim 14, further comprising: providing a first member in thecasting pattern; providing a second member in the casting pattern; andremoving the first member aid the second member after said solidifying.24. The method of claim 14, wherein the formed structure has the entirehigh thermal conductivity member provided within the solidified moltenalloy.
 25. The method of claim 14, wherein said solidifying includesdirectionally the molten alloy.